Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session Y9: Nuclear Astrophysics |
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Sponsoring Units: DNP Chair: Micha Kilburn, University of Notre Dame Room: Governor's Square 11 |
Tuesday, April 16, 2013 1:30PM - 1:42PM |
Y9.00001: Nuclear Pasta Properties from Molecular Dynamics Simulations Andre da Silva Schneider, Joe Hughto, Charles Horowitz, Don Berry The physics of matter at subnuclear densities, about $10^{13}$ to $10^{14}$ g/cm$^3$, is relevant to understand some of the properties of neutron star crusts and supernovae explosions. At such high densities, because of competition between attractive short-range nuclear forces and repulsive long-range Coulomb forces, it is expected that nucleons arrange themselves in a variety of complex shapes known as \textit{nuclear pasta}. We study \textit{nuclear pasta} at a range of densities and proton fractions using large scale molecular dynamics simulations with a simple semiclassical model for the nucleon interactions. From our simulations we calculate the structure factor of different pasta configurations, which are relevant for neutrino opacities in supernovae. From these simulations we can also obtain some mechanical properties of the pasta, such as shear modulus, bulk viscosity and breaking strains. These can help determine the frequency of shear modes in neutron star crusts and the size of mountains the crust can support. [Preview Abstract] |
Tuesday, April 16, 2013 1:42PM - 1:54PM |
Y9.00002: Neutrino opacity for astrophysics Gang Shen, Luke Roberts, Vincenzo Cirigliano, Sanjay Reddy Neutrino interactions with dense matter dictate the long time evolution of compact remnants in core-collapse supernova (CCSN) and binary neutron star mergers (BNS). In this talk I will describe our work on neutrino opacity in the hot dense matter, which is suitable for use in astrophysical simulations of compact remnants. We include the nuclear medium corrections to the neutrino opacity, which is consistent with underlying nuclear equation of state (EOS). We also include a relaxation time scheme to account for medium corrections beyond conventional one-particle-hole excitation, which is not constrained by EOS. [Preview Abstract] |
Tuesday, April 16, 2013 1:54PM - 2:06PM |
Y9.00003: Generic conditions for stable hybrid stars Sophia Han, Mark Alford, Madappa Prakash We study the stability and maximum mass of hybrid stars, assuming a generic quark matter equation of state with a first-order phase transition between nuclear and quark matter, and a sharp interface between the quark matter core and nuclear matter mantle in a neutron star. For standard nuclear matter equations of state, we find that the mass-radius relation contains a stable hybrid branch, connected to the nuclear matter star branch, if the energy density discontinuity at the nuclear-quark transition is less than a critical value, which is typically between 60\% and 80\% of the nuclear matter energy density at the transition. Extending the quark matter EoS to higher densities by assuming it has an ideal gas form, we find that, as has been noticed before, there can be a second disconnected branch of hybrid stars. For typical nuclear matter equations of state, this branch exists if the nuclear matter density at the transition is less than a critical value which is about two to four times nuclear saturation density. We calculate the maximum hybrid star mass as a function of the nuclear matter density and the parameters of the quark matter EoS, and find that hybrid stars with mass above $2\,M_\odot$ can exist. [Preview Abstract] |
Tuesday, April 16, 2013 2:06PM - 2:18PM |
Y9.00004: Inelastic Scattering of Alphas on Mg-24 as a Surrogate for Stellar Carbon Burning Justin Munson, Eric Norman, Jason Burke, Larry Phair, Robert Casperson, Matt McCleskey, Perry Chodash, Richard Hughes, Ellen McCleskey, Roby Austin, Antti Saastamoinen, Alex Spiridon, Roman Chyzh, Shamsuzzoha Basunia, Timothy Ross, Jennifer Ressler Inelastic excitation of $^{24}Mg$ is used as a surrogate for $^{12}C+^{12}C$ burning at stellar energies. The branching ratio for $^{12}C+^{12}C\rightarrow^{20}Ne+\alpha$ and $^{12}C+^{12}C\rightarrow^{23}Na+p$ is determined by the decay channel ratio of the excited $^{24}Mg$. Experiments were performed using the 88'' cyclotron at LBNL and the 88'' cyclotron at the Texas A\&M Cyclotron Institute using a 40 MeV alpha beam on a Mg target. The scattered alpha and the ejected alpha or proton were detected using Si detectors while gammas from the often excited daughters were detected using germanium ``clover'' detectors. This is called the STARS/LiBerACE array at LBNL and the STARLiTe array at Texas A\&M. This work was supported in part at LBNL by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Division of Nuclear Physics, of the U.S. Department of Energy under Contract DE-AC02-05CH11231; LLNL under Contract DE-AC52-07NA27344; and Texas A\&M under DOE Office of Nuclear Physics grant DE-FG02-93ER40773 and NNSA grant DE-FG52-09NA29467. [Preview Abstract] |
Tuesday, April 16, 2013 2:18PM - 2:30PM |
Y9.00005: Prospects of Optical Single Atom Detection in Noble Gas Solids for Measurements of Rare Nuclear Reactions Jaideep Singh, Kevin G. Bailey, Zheng-Tian Lu, Peter Mueller, Thomas P. O'Connor, Chen-Yu Xu, Xiaodong Tang Optical detection of single atoms captured in solid noble gas matrices provides an alternative technique to study rare nuclear reactions relevant to nuclear astrophysics. I will describe the prospects of applying this approach for cross section measurements of the $^{22}\mathrm{Ne}\,(\alpha,n)\,^{25}\mathrm{Mg}$ reaction, which is the crucial neutron source for the weak $s$ process inside of massive stars. Noble gas solids are a promising medium for the capture, detection, and manipulation of atoms and nuclear spins. They provide stable and chemically inert confinement for a wide variety of guest species. Because noble gas solids are transparent at optical wavelengths, the guest atoms can be probed using lasers. We have observed that ytterbium in solid neon exhibits intersystem crossing (ISC) which results in a strong green fluorescence (546 nm) under excitation with blue light (389 nm). Several groups have observed ISC in many other guest-host pairs, notably magnesium in krypton. Because of the large wavelength separation of the excitation light and fluorescence light, optical detection of individual embedded guest atoms is feasible. This work is supported by DOE, Office of Nuclear Physics, under contract DE-AC02-06CH11357. [Preview Abstract] |
Tuesday, April 16, 2013 2:30PM - 2:42PM |
Y9.00006: Spectroscopy of $^{86,87,88}$Se levels populated through beta decay of $^{86,87,88}$As J. Pereira, W.B. Walters, M.K. Smith, A. Aprahamian, C.J. Chiara, A. Gade, T. Ginter, G. Hackman, N. Larson, S.N. Liddick, C. Prokop, H. Schatz, O.B. Tarasov The overabundances of Sr, Y and Zr elements observed in some r-process-enriched, metal-poor stars complicate the quest for the r-process site. Jones et al$. $[Phys. Rev. C73, (2006)] reported an anomalously high 886-keV E(2$+)$ in $^{88}$Se$_{54}$ , which may be related to a doubly-magic $^{90}$Se$_{56}$. This new waiting point might explain the Sr, Y, Zr overabundances. A new experiment was carried out at NSCL to measure the structure of neutron-rich Se isotopes. New spectroscopic information of $^{86,87,88}$Se has been obtained through the beta decay of $^{86,87,88}$As nuclei. A gamma ray at 93 keV has been observed in the decay of $^{87}$As that could arise from the transition 5/2$^{+}$ to 3/2$^{+}$, as observed in the higher-Z N $=$ 53 isotones. A gamma-ray transition at 651 keV has been observed in the decay of $^{88}$As that could be a part of the yrast cascade in $^{88}$Se. The 886 keV gamma-ray observed by Jones et al. could not be verified. [Preview Abstract] |
Tuesday, April 16, 2013 2:42PM - 2:54PM |
Y9.00007: Experimental Results of the $^{33}$S($\alpha$,p)$^{36}$Cl Cross Sections: Implications on $^{36}$Cl Production in the Early Solar System Matthew Bowers, Philippe Collon, Yoav Kashiv, William Bauder, Wenting Lu, Karen Ostdiek Isotopic measurements of primitive solids in meteorites provide insight into the origins of the Solar System, the chemical evolution of the elements, and nucleosynthetic processes. Identifying the origins of now-extinct short-lived radionuclides (SLRs) is important for both Early Solar System chronology and nuclear astrophysics. The origin of extinct $^{36}$Cl in the early Solar System is thought to have been produced by irradiation of gas and dust by solar energetic particles emitted by the young Sun. Attempts to recreate the production of $^{36}$Cl in the early Solar System using the x-wind model lack experimental data for the nuclear reactions considered. We measured the cross sections for the $^{33}$S($\alpha$,p)$^{36}$Cl reaction, an important reaction in the production of $^{36}$Cl, at six energies that ranged from 0.70-2.42 MeV/A. The cross section measurement was performed by bombarding a target and collecting the recoiled $^{36}$Cl atoms produced in the reaction, chemically processing the samples, and measuring the $^{36}$Cl/Cl concentration with AMS. The experimental procedure, results, and comparison with predicted Hauser-Feshbach predictions will be discussed. [Preview Abstract] |
Tuesday, April 16, 2013 2:54PM - 3:06PM |
Y9.00008: Measuring radiative capture rates at DRAGON U. Hager, B. Davids, J. Fallis, U. Greife, D.A. Hutcheon, A. Rojas, C. Ruiz The DRAGON recoil separator facility is located at the ISAC facility at TRIUMF, Vancouver. It is designed to measure radiative alpha and proton capture reactions of astrophysical importance in inverse kinematics. The Supernanogan ion source at ISAC provides stable beams of high intensities. The DRAGON collaboration has taken advantage of this over the last years by measuring several reactions requiring high-intensity stable oxygen beams. In particular,the $^{17}$O($p$,$\gamma$) and $^{16}$O($\alpha$,$\gamma$) reaction rates were recently measured. The former reaction is part of the hot CNO cycle, and strongly influences the abundance of $^{18}$F in classical novae. Because of its relatively long lifetime, $^{18}$F is a possible target for satellite-based gamma-ray spectroscopy. The $^{16}$O($\alpha$,$\gamma$) reaction plays a role in steady-state helium burning in massive stars, where it follows the $^{12}$C($\alpha$,$\gamma$) reaction. At astrophysically relevant energies, the reaction proceeds exclusively via direct capture, resulting in a low rate. In both cases, the unique capabilities of DRAGON enabled determination not only of the total reaction rates, but also of decay branching ratios. Results from both experiments will be presented. [Preview Abstract] |
Tuesday, April 16, 2013 3:06PM - 3:18PM |
Y9.00009: From a complex scalar field to the two-fluid picture of superfluidity S. Kumar Mallavarapu, Mark Alford, Andreas Schmitt, Stephan Stetina In the field theoretic formulation of a zero-temperature superfluid one connects the superfluid four-velocity which is a macroscopic observable with a microscopic field variable namely the gradient of the phase of a Bose-Condensed scalar field. On the other hand, a superfluid at nonzero temperatures is usually described in terms of a two-fluid model: the superfluid and the normal fluid. In this talk we offer a deeper understanding of the two-fluid model by deriving it from an underlying microscopic field theory. In particular, we shall obtain the macroscopic properties of a uniform, dissipationless superfluid at low temperatures and weak coupling within the framework of a $\varphi^4$ model. Though our study is very general, it may also be viewed as a step towards understanding the superfluid properties of various phases of dense nuclear and quark matter in the interior of compact stars [Preview Abstract] |
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